Apparatus for and method of detecting and measuring corrosion damage in pipe

Abstract

Apparatus for and a method of detecting and measuring the presence and degree of corrosion damage in pipe by using a probe which forms a capacitor with the wall of the pipe is disclosed. The probe is moved interior to and longitudinally of the pipe, and the variation in capacitance occuring whenever the probe passes a corrosion portion of the interior pipe wall is detected.

I claim: 
     
       1. Apparatus for detecting corrosion damage to electrically conductive pipe, comprising: (a) a movable conductive ring within said pipe; and   (b) means for moving said conductive ring longitudinally of said pipe; said conductive ring and the wall of said pipe forming the electrodes of a varying electrical capacitance means such that the capacitance of said varying capacitance means changes whenever said movable conductive ring passes a corrosion portion of the inner pipe wall; and     (c) means electrically connected to said varying capacitance means for detecting the variations in its electrical capacitance.   
     
     
       2. The apparatus of claim 1, further comprising: (d) means electrically connected to said detecting means for displaying the detected variations in the capacitance of said varying electrical capacitance means.   
     
     
       3. The apparatus of claim 2, wherein said detecting means comprises an electrical bridge circuit having a plurality of arms and exciting means electrically connected to said bridge circuit, said varying capacitance means forming one arm of said bridge circuit, said bridge circuit being constructed such that its unbalanced output changes whenever said movable conductive ring passes a corrosion portion of the inner pipe wall. 
     
     
       4. The apparatus of claim 2, wherein said detecting means comprises an electrical resonant circuit and exciting means electrically connected to said resonant circuit, said resonant circuit being adjusted such that resonance is established whenever said movable conductive ring is not passing a corrosion portion of the inner pipe wall and resonance is disestablished whenever said movable conductive ring passes a corrosion portion of the inner pipe wall. 
     
     
       5. The apparatus of claim 2, further comprising: (e) constant electrical capacitance means circuit connected to said variable capacitance means, said circuit connected combination of constant and varying capacitance means being electrically connected to said detecting means.   
     
     
       6. The apparatus of claim 2, further comprising: (e) means electrically connected between said detecting means and said display means for rectifying the output of said detecting means before said output is displayed by said display means.   
     
     
       7. Apparatus for detecting corrosion damage to electrically conductive pipe, comprising: (a) a plurality of conductive members;   (b) non-conductive means for carrying said plurality of conductive members, said carrier means and said conductive members being located interior to and being movable longitudinally of said pipe, said conductive members being positioned substantially symmetrically and substantially uniformly over the outer surface of said carrier means; and   (c) means interacting with said carrier means for moving said plurality of conductive members longitudinally of said pipe; each said conductive member and the wall of said pipe forming the electrodes of a varying electrical capacitor such that the capacitance of each said varying capacitor changes whenever the associated conductive member of said plurality of conductive member passes a corrosion portion of the inner pipe wall;     (d) a first varying capacitance means comprised of said varying electrical capacitors formed by said plurality of conductive members and the pipe wall; and   (e) first detecting means electrically connected to said first varying capacitance means for detecting the variations in its electrical capacitance.   
     
     
       8. The apparatus of claim 7, further comprising: (f) first display means electrically connected to said first detecting means for displaying the detected variations in the capacitance of said first varying electrical capacitance means.   
     
     
       9. The apparatus of claim 8, wherein said first detecting means further comprises means for detecting the maximum variation in the capacitance of the varying electrical capacitors of said first varying electrical capacitance means formed by each said of said plurality of conductive members and said pipe, and wherein said first display means further comprises means for displaying said maximum variation in capacitance. 
     
     
       10. The apparatus of claim 9, wherein said means for detecting the maximum variation in capacitance of the individual electrical capacitors of said first varying electrical capacitance means comprises a logical "OR" circuit. 
     
     
       11. The apparatus of claim 8, further comprising: (g) a second movable conductive member interior to said pipe affixed to and substantially encircling a portion of said carrier means, said conductive member and the wall of said pipe forming the electrodes of a second varying electrical capacitance means such that the capacitance of said varying capacitance means changes whenever said conductive member substantially encircling a portion of said carrier means passes a corrosion portion of the inner pipe wall;   (h) second detecting means electrically connected to said second varying capacitance means for detecting the variations in its electrical capacitance; and   (i) second display means electrically connected to said second detecting means for displaying the detected variations in the capacitance of said second varying electrical capacitance means.   
     
     
       12. A method for detecting corrosion damage to electrically conductive pipe, comprising: (a) forming a varying electrical capacitor using the pipe as an electrode of said capacitor and a conductive ring movable within said pipe as another electrode of said capacitor;   (b) moving said conductive member interior to and longitudinally of said pipe; and   (c) detecting with electrical circuit means the variations in the capacitance of said varying electrical capacitor occurring whenever said moving conductive member passes a corrosion portion interior to said pipe.   
     
     
       13. The method of claim 12, further comprising: (d) displaying the detected variations in the capacitance of said varying capacitor.   
     
     
       14. A method for detecting corrosion damage to electrically conductive pipe, comprising: (a) forming a plurality of first varying electrical capacitors using the pipe as one electrode of each of said plurality of first capacitors, and one of a plurality of first movable conductive members in said pipe as another electrode of each of said plurality of first capacitors; said plurality of first conductive members being substantially uniformly and substantially symmetrically positioned over the surface of an insulating cylindrical member in the pipe;   (b) moving said plurality of first conductive members and said cylindrical member longitudinally of the pipe; and   (c) detecting with electrical circuit means the changes in the capacitance of said first varying capacitors.   
     
     
       15. The method of claim 14, wherein the detecting of the variations in the capacitance of said first varying capacitors further comprises detecting the maximum variation in the capacitance of said first varying capacitors. 
     
     
       16. The method of claim 14, further comprising: (d) displaying the detected variations in the capacitance of said first varying capacitors.   
     
     
       17. The method of claim 16, further comprising: forming a second varying electrical capacitor using the pipe as one electrode and a second movable conductive member in the pipe substantially encircling said insulating cylindrical member in the pipe as another electrode of said second varying capacitor; wherein the moving of said plurality of first conductive members and said cylindrical member longitudinally of the pipe further comprises moving said second conductive member longitudinally of the pipe; wherein the detecting of the changes in the capacitance of said first varying capacitors further comprises detecting the changes in the capacitance of said second varying capacitor; and wherein the displaying of the detected variations in the capacitance of said first varying capacitors further comprises displaying the detected variations in the capacitance of said second varying capacitor.   
     
     
       18. A probe for detecting corrosion damage to electrically conductive pipe, comprising: (a) a non-conductive cylindrical member having an outside diameter less than that of the inside diameter of the pipe, said cylindrical member being adapted and constructed to be movable within said pipe longitudinally of the pipe;   (b) a pair of insulating rings, one encircling each end of said cylindrical member, the outside diameter of each said ring being slightly less than the inside diameter of said pipe; and   (c) a first conductive member substantially encircling said cylindrical member between said insulating rings, the outside diameter of said first conductive member being less than that of said insulating rings, said first conductive member being arranged and adapted to form with the wall of said pipe the electrodes of a first varying electrical capacitance whose capacitance changes whenever said first conductive member passes a corrosion portion of the inner pipe wall as said cylindrical member is moved within said pipe longitudinally of the pipe.   
     
     
       19. The probe of claim 18, further comprising: (d) a conductive shielding member encircling a substantial portion of said cylindrical member not including said first conductive member, said shielding member forming with said pipe the electrodes of a constant electrical capacitance electrically circuit connected to said first varying capacitance formed by said first conductive member and said pipe.   
     
     
       20. The probe of claim 18, further comprising: (d) first detecting means electrically connected to said first varying capacitance means for detecting variations in the capacitance of said first varying capacitance means, said detecting means being built into said cylindrical member.   
     
     
       21. The probe of claim 20, further comprising: (e) a plurality of second conductive members substantially uniformly and substantially symmetrically positioned over the surface of said cylindrical member, each of said second conductive members forming with said pipe the electrodes of one of a plurality of second varying capacitances, the capacitance of each of said plurality of second varying capacitances changing whenever the associated second conductive member passes a corrosion portion of the inner pipe wall as said cylindrical member is moved within said pipe longitudinally of the pipe; and   (f) second detecting means for detecting variations in the capacitance of said plurality of second varying capacitances, said second detecting means being built into said cylindrical member.   
     
     
       22. The probe of claim 21, wherein said second detecting means built into said cylindrical member further comprises means for detecting the maximum variation in the capacitances of said plurality of second varying capacitances. 
     
     
       23. The probe of claim 22, wherein said means built into the cylinder member for detecting the maximum variation in the capacitances of said second varying capacitances comprises a logical "OR" circuit. 
     
     
       24. Apparatus for detecting the presence and degree of corrosion damage to electrically conductive pipe, comprising: (a) a first conductive member movable within said pipe;   (b) means for moving said conductive member within said pipe, longitudinally of the pipe;   (c) electrical means circuit connected between said first conductive member and said pipe for establishing an electric field between said first conductive member and the walls of said pipe, the lines of force of said electric field impinging on a substantial portion of the inner circumference of said pipe wall; said conductive member, said electrical circuit means and said pipe forming a first varying electrical capacitance such that the capacitance of said first varying capacitance changes when said first movable conductor passes a corrosion portion of said inner pipe wall; and   (d) first detecting means electrically connected to said first varying capacitance for detecting the changes in its electrical capacitance.   
     
     
       25. The apparatus of claim 24, further comprising: (e) a plurality of second conductive members adapted to be located interior to and moved longitudinally of said pipe;   (f) means for moving said plurality of second conductive members within said pipe, longitudinally of the pipe, simultaneously with the moving of said first conductive member longitudinally of said pipe;   (g) electrical means circuit connected between said plurality of second conductive members and said pipe for establishing an electric field between each of said conductive members and the walls of said pipe, the lines of force of said electrical field associated with each conductive member of said plurality of second conductive members impinging on a segment of the inner circumference of said pipe wall; said plurality of second conductive members, said electrical circuit means and said pipe forming a plurality of second varying capacitances such that the capacitance of each such varying capacitance changes when the associated conductive member of the plurality of second conductive members passes a corrosion portion of the inner pipe wall; and   (h) second detecting means electrically connected to said plurality of second varying capacitances to detect the changes in its electrical capacitance.